Refactor delta computation to be DAG based (#727)

Signed-off-by: Juan Cruz Viotti <[email protected]>

Author: jviotti

src/build/CMakeLists.txt

@@ -1,6 +1,6 @@
 sourcemeta_library(NAMESPACE sourcemeta PROJECT one NAME build
   PRIVATE_HEADERS state.h
-  SOURCES delta.cc state.cc)
+  SOURCES rules.h delta.cc state.cc)
 target_link_libraries(sourcemeta_one_build
   PUBLIC sourcemeta::core::json sourcemeta::one::resolver
   PRIVATE sourcemeta::core::io)